The peroxidative reactions of hemoglobin (Hb) and myoglobin (Mb) constrain delivery and turnover of oxygen to cells. The reactions of these proteins with hydrogen peroxide (H2O2) and its superoxide anions are detrimental in red cell pathological conditions, i.e. sickle cell anemia, thalassemia, and red cell aging. These reactions limit the development of proteins for oxygen carrying therapeutics. The formation of ferryl (hemeFe(IV)=O) species have been identified as one of the main reaction intermediates. Interactions of these species with a number of Hb and Mb heme pocket amino acids are also known. Despite the efforts, concerns persist about the transient structure, mechanism, kinetics, dynamics, and reactivity of Hb and Mb with H202. The relationship between the structure, reactivity, and function of these Hb and Mb ferryl derivatives is not clearly understood. An answer to these problems will unravel the nature of the ferryl species and their relationship to heme peroxidative reactions. Our preliminary studies show that we will achieve this goal by taking advantage of the ability of hemoglobin I (Hbl) from L. pectinata to stabilize, through its unusual heme pocket configuration (Gin64, Phe29, and Phe68), the ferryl (hemeFe(IV)=O) compound I a thousand times more than Mb. This suggest that the interplay between the proximal transligand effect, the distal heme pocket polarizability, and the absence of hydrogen bonding between the distal amino and the ferryl are also responsible for such behavior. Here we will address these issues by continuing our previous work on mutated Hbl species and following the formation of their heme-ferryl derivative by time resolved resonance Raman. These techniques can detect the transient ferryl species in times shorter than milliseconds and can help resolve questions such as: How does H2O2 ligand stabilization occur? Which conformational and structural changes are important in the stabilization of HblFe(IV)=O ferryl? What control heme and H202 reactivity in this unique protein? How do the heme pocket aromatic residues contribute or modulate the association and dissociation rate constants for ferryl intermediates in Hbl or Hbll?